I have a group that I can essentially no longer add email addresses to. The problem started as soon as I hit 100 external email addresses in the group. From that point on, almost every time I try to add a new external address the Email Address textarea clears and the the record count in the top-right changes to "NaN." I then search for the email address and it hasn't been added. Very occasionally it works and it will let me add one or two email addresses before the bug returns. I have another 30 or so email addresses to add. At this rate it's going to take another week.

I have tried this in Chrome, Firefox and IE and it behaves the same way in all of them. Therefore, it's clearly an application bug and not a browser bug. 

Also, I tried importing all the remaining emails at once (comma separated) but, on the rare occasion when I don't get the "NaN" message, it just imports the first address and ignores the others.

This is supposed to be fully set up for a client by Monday. It's now Friday. Quite frankly, it would have been a deal breaker had I known about it beforehand.